1. Field of the Invention
This invention relates to harvesting kinetic energy of rivers and ocean tidal currents in shallow waters and it is based on the utilization of Darrieus type turbines.
2. Discussion of Prior Art
The most of the known installations for harvesting kinetic energy of the water streams, which are originated by tides or rivers in shallow waters, are of two types. One type is using Propeller-turbines with horizontal axis of rotation the other type is using Darrieus hydro-turbines with vertical orientation of their axis of rotation. The specific of Darrieus hydro-turbines is that they rotate always in one direction, regardless of water flow direction. The propeller-turbines, in case of their application for harvesting tidal energy, have to have special provisions to accommodate 180° change in the direction of water flow.
The propeller-turbines type installation have horizontal axis of rotation and usually are located bellow water level on the sea or river bottom. Thus allows timber rafting and ice drifting to flow above them and also to minimize effect of waves actions on their structures. However, since the multiplicator and generator are on the same axis with propeller and are located underwater, this requires placing them in hermetic capsule. The need for hermetic capsule, besides significant complication of performing regular maintenance, creates the possibility of multiplicator some day flooding. Thus makes the systems requiring use hermetic capsule not reliable for a prolong use.
The vertical orientation of Darrieus type turbines allows locating their multiplicator and generator above water and by this providing advantage of simplifying the process of their maintenance. Also advantage of Darrieus turbine versus propeller-turbines is that in cases when depth of water limits the size of turbine the square shape of Darrieus turbine has about 20% larger area. These advantages in many cases outweigh the drawback of being obstacle to timber rafting and ice drifting.
The Darrieus type turbine that was patented in 1927 (U.S. Pat. No. 1,835,018) was widely used for harvesting kinetic energy of the wind. Only in the beginning of 1980ries the Canadian Company Nova Energy, Ltd. pioneer used of Darrieus turbines for harvesting energy of water streams. Their basic design (see website—bluenergy.com) utilizes vertically oriented turbine into a frame that is connected to the sea bottom. This limits their use to shallow water straits and rivers.
The other company that presently uses Darrieus turbine in their projects is GCK Technologies Inc. Its systems are described in the U.S. Pat. No. 6,036,443, issued to Alexander Gorlov. Specific of this patented turbine is in the use of helical blade instead of conventional straight blade of Darrieus turbine. The goal of using helical blade is to provide to turbine self-staring capability. Presently all 2 and 3 blades Darrieus turbines used for harvesting wind energy and converting it to electricity are started by a motor. Since this motor, after turbine reaches synchronous speed of AC power in the grid, starts to operate, as generator the absence of self-starting capability is not a problem at all for systems supplying electricity in power grid.
Installations for harvesting kinetic energy of water streams shown in Gorlov U.S. Pat. No. 6,036,443 are located underwater, thus making them vulnerable for flooding and are not accessible for frequent maintenance. Gorlov also came up with submerged floating system that can be anchored in deep waters to sea bottom by mooring lines. This floating system is described in article “Helical Turbines for the Gulf Stream: Conceptual Approach to Design of a Large-Scale Floating Power Farm”, see Marine Technology, Vol. 35, July 1998, pp. 175-182.
The US Patent Installation for Harvesting Ocean Currents (IHOC) U.S. Pat. No. 6,856,036 B2, issued on Feb. 15, 2005 to Sidney Belinsky, who is also author of instant invention, illustrates application of vertically oriented Darrieus turbine for harvesting energy of ocean currents in deepwaters. It also it illustrates use of funnel in combination with turbine, which increases the speed of water passing through the turbine. The turbine wheel design consists of 3 two-straight blade turbines staggered on 120 degrees and assembled on one shaft. Thus forms a six-blades turbine that has the self-starting capability and delivers smoother torque distribution during one rotation. At the same time two-blade Darrieus turbine have higher efficiency that 3-4 blades turbines used by Blue Energy Canada and GCK Technology, Inc.